A foundation earth consists of non-insulated conductors usually made of strip or round steel, which is embedded in the foundations of the outer walls or in the baseplate of the building and over the relatively well conductive concrete over a large area in contact with the earth.
It shall be designed as a closed ring and connected to the main equipotential bonding rail, usually in the service connection room, via a conspicuously marked, corrosion-protected connection lug (hot-dip galvanized steel with plastic jacket or stainless steel) of at least 1.50 m in length. For the lightning protection further connection lugs are to be provided.
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| Foundation earthing is made under a building to ensure the electrical safety. |
The galvanized or non-galvanized steel must be surrounded on all sides by at least 5 cm of concrete. Thus, a high corrosion resistance is achieved, which practically corresponds to the life of the building. Round steel should be at least 10 mm in diameter. Strip steel (mimimum 30 mm x 3.5 mm or 25 mm x 4 mm) must be laid edgeways.
Electrically reliable connections are achieved by welding, screw or clamp connections. Twisted joints are inadmissible. Expansion joints in the foundation must be bridged with expansion bands.
For large buildings, according to DIN 18014, foundation earthing - planning, execution and documentation is recommended to divide the covered base area by conductive cross connections in mesh sizes of about 20 m x 20 m. In terraced houses under each house should be formed according to the size of the plot a small closed ring. The grounding resistance of the founding earth of a detached house is generally between 2 ohms and 6 ohms.
Note:
In the case of "white concrete trough ( water-impermeable concrete), "black trough" (sealed with bitumen) or a trough with perimeter insulation (thermal insulation), a ring ground electrode is required for reliable connection with the earth, which is arranged outside the foundation concrete (but near the foundation) This ring electrode must be protected against corrosion according to DIN 18014 Foundation earth (stainless steel), since it is not covered by concrete.
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